I could swear the new dev team stated or hinted strongly every class will eventually come out with more then one job. As for example as someone said, Pld or Drk.
They said for now, as the release of the concept of jobs, only one job a class. Thats only due to you can only release so much at one time.
If they DIDNT do this down the long road, classes would be completely pointless, as jobs take up the class 95% of the time.